Lubricating compositions and antioxidants therefor



United States Patent 3,376,224 LUBRICATING COMPOSITIONS AND ANTIOXIDANTS THEREFOR John Scotchford Elliott, Eric Descamp Edwards, and Anthony David Brazier, London, England, assignors to Castrol Limited, London, England, a British company No Drawing. Filed May 18, 1964, Ser. No. 368,407 Claims priority, application Great Britain, May 24, 1963, 20,934/ 63 12 Claims. (Cl. 252-475) The invention relates to lubricating compositions and in particular to such compositions comprising as antioxidants phenothiazine derivatives which are, in certain cases, new compounds.

Phenothiazine derivatives have been disclosed which have the formula:

in which R represents an alkyl or cycloalkyl radical which may carry an alkoxy or other non-reactive substituent. It has further been disclosed that such new compounds and solutions in oil are useful for pharmaceutical veterinary and pest control purposes. However, there has been no disclosure of the use of compounds of this type as ingredients of lubricating compositions.

According to the present invention there is provided a lubricating composition comprising a major amount of lubricating oil, i.e., an oil of lubricating viscosity, or grease together with a phenothiazine derivative having the general formula where Ar and Ar are benzene or naphthalene nuclei and R is an alkyl, aryl, alkaryl, aralkyl, cycloalkyl, alkoxy alkyl, cycloalkoxy alkyl or aryloxy alkyl radical. The phenothiazine derivative may carry alkyl or alkoxy substituents attached to the aromatic nuclei if desired.

In a preferred form of the invention the phenothiazine derivative has the general formula:

onion where R and R are H or alkyl radicals, the sum of the carbon atoms in R and R being from 4-24.

We have found that these phenothiazine derivatives are particularly useful as antioxidants in lubricating compositions based on mineral lubricating oils as well as in synthetic lubricants of various types, e.g., in the wellknown neutral organic dicarboxylic acid diesters or in the so-called hindred esters which are derived from dior polyhydric alcohols having no hydrogen atoms on the carbon atom in the ,8-position to the hydroxyl groups. They are also effective antioxidants in lubricating compositions based on polyglycol ethers.

Whilst these phenothiazine derivatives are effective antioxidants for synthetic ester-based lubricants when used on their own, their efficiency may be considerably enhanced by employing them in conjunction with one or more secondary aromatic amines containing two aromatic groups directly attached to nitrogen, the two additives acting synergistically to provide greater resistance to oxidation at elevated temperatures than would be provided by either additive used by itself in comparable proportions.

In the past, phenothiazine has been used with considerably success as an antioxidant for synthetic ester-based gas turbine lubricants but has suffered from the disadvantage that it becomes itself oxidised to insoluble oxidation products which accumulate as sludge. This phenothiazine dirtiness has often been the factor which has limited the performance of an oil in service and, in some engines, determined the length of time between overhauls.

The problem of phenothiazine dirtiness has been successfully overcome by the use, instead of phenothiazine itself, of phenothiazines containing alkyl or alkoxy substituents directly attached to one or both of the benzene rings, these substituents containing a total of at least 8 carbon atoms in the alkyl or alkoxy groups. In order to provide adquate bulk oil oxidation resistance at the temperature encountered in aircnaft gas turbine engines, it has been necessary to employ these compounds in conjunction with one or more secondary aromatic amines. Typical synergistic combinations of antioxidants of this type are 3,7-dioctyl phenothiazine with pp dioctyl diphenylamine or phenyl-a-naphthylamine.

Synthetic diester-based lubricants containing additive combinations of the foregoing type have given very satisfactory performance at maximum bulk oil temperatures of up to 350-375 F, and have been extremely clean in operation. With the advent of supersonic aircraft, however, and the considerably higher maximum bulk oil temperatures attained (e.g., 450 F. for the so-called Type II oils) it is necessary to provide not only base stocks of higher thermal and oxidation stability but also superior antioxidants.

We have found that the phenothiazine derivatives of the present invention, when used in conjunction with secondary aromatic amines of the type described, in hindered ester base stocks, are capable of providing lubricants having superior oxidation resistance at temperatures of the order of 450 F. to similar lubricants containing phenothiazine or phenothiazine derivatives of the prior art.

While we do not wish to be restricted by any theory, we believe that the phenothiazine derivatives of the present invention function by means of a two-stage break down mechanism, initially furnishing (llH radicals, these two radicals together providing the oxidation resistance required. We believe that the compounds of the present invention are more effective antioxidants in the range 400-4 50 F. than phenothiazine or nuclear alkylated phenothiazines because the NCH bond is more resistant to oxidation than the NH bond and therefore the side reactions involving the direct oxidation of the compound take place to a lesser degree.

Whilst those compounds having the general formula given above in which Ar and Ar are unsubstituted benzene nuclei are very effective antioxidants and superior to phenothiazine in the 400-450 F. temperature range, they are prone to give rise to sludge on oxidation since, in the long run, the same degradation products are formed as those emanating from phenothiazine itself. In order to provide both good oxidation resistance and freedom from sludge formation, it is therefore preferred to employ compounds having the formula:

where R is an alkyl radical, and R is H or an alkyl radical, the sum of the carbon atoms in R and R being at least 4 and preferably at least 8. Compounds having this formula are believed to be new compounds, not heretofore prepared or described.

The present invention therefore includes, as new compounds, thiazines having the general formula:

(II-DOB where Ar and Ar are benzene or naphthalene nuclei, R is an alkyl, aryl, alkaryl, aralkyl, cycloalkyl, alkoxyalkyl, cycloalkoxyalkyl or aryloxyalkyl radical, R is an alkyl radical, R is H or an alkyl radical and the sum of the carbon atoms in R and R is from 8 to 24.

Preferably Ar and Ar are both benzene nuclei, R and R are both tertiary octyl radicals and R is an alkyl or cycloalkyl radical having from 1-20 carbon atoms, the compounds being derived from 3,7-dioctyl phenothiazine.

A preferred form of the invention relates to lubricating compositions which are suitable for use as high temperature gas turbine lubricants, such compositions being based upon synthetic organic carboxylic esters. Accordingly, in a preferred form of the invention, a lubricating composition comprises a major proportion of a synthetic organic lubricating oil based upon neutral organic carboxylic esters, which esters are preferably of the so-called hindered ester type and a minor proportion of two additives (a) and (b), additive (a) being a phenothiazine derivative as defined above and additive (b) being a secondary aromatic amine which contains two aromatic groups directly attached to nitrogen. The secondary aromatic amine which is preferred is phenyl-u-naphthylamine but alternative amines which may be used are phenyl-B-naphthylamine, pp-dioctyl diphenylamine, pmono-octyl diphenylamine, mixed heptyl diphenylamines or compounds having the formula:

where Ar represents a benzene neucleus, Ar represents a benzene or naphthalene nucleus (both Ar and Ar may contain alkyl substituents), R and R" are saturated alkyl radicals preferably containing a total of from 8 to 20 carbon atoms, m is 1 or 2 and n is zero or 1. It may be desirable to employ more than one secondary aromatic amine.

It is preferred that group R of the phenothiazine derivative is derived from a primary alcohol ROH having from 1 to 12 carbon atoms.

In a particularly preferred form of the invention, a lubricating composition comprises a major proportion of a synthetic organic lubricating oil based upon one or more neutral esters of trimethylol propane, pentaerythritol or dipentaerythritol and monocarboxylic acids having from four to ten carbon atoms together with a minor proportion of two additives (a) and (b), additive (a) being a phenothiazine derivative as defined present in an amount sufficient to provide from 0.04 to 0.15% of sulphur in the composition and additive (b) being a secondary aromatic amine which contains two aromatic groups directly attached to nitrogen present in an amount sufficient to provide from 0.1 to 0.2% of nitrogen in the composition.

Preferably additive (a) is an N-alkoxymethyl or N- cycloalkoxymethyl derivative of 3,7 dioctyl phenothiazine derived from a primary alcohol ROH having from 1-20 carbon atoms in the radical R and additive (b) is phenyl-u-naphthylamine.

Specific examples of phenothiazine derivatives in accordance with the invention are N-ethoxymethyl phenothiazine N-n-butoxymethyl phenothiazine N-n-hexoxymethyl phenothiazine N-1,3,dimethyl butoxymethyl phenothiazine N-n-decoxymethyl phenothiazine N-n-dodecoxymethyl phenothiazine N-methoxy-methyl 3-n-butoxy phenothiazine N-n-hexoxymethyl S-n-decoxy phenothiazine.

Specific examples of the preferred thiazine derivatives (which are new compounds) are:

Specific examples of additives (b) are Phenyl-a-naphthylamine Phenyl-fl-naphthylamine pp-Dioctyl diphenylamine p-Monooctyl diphenylamine Mixed octylated diphenylamines Mixed heptylated diphenylamines p-Isopropoxydiphenylamine p-n-Butoxydiphenylamine Diphenyl-p-phenylene diarnine p-n-octoxy diphenylamine p-n-decoxy diphenylamine p-n-dodecoxy diphenylamine p-n-hexadecoxy diphenylamine p-(3 15:5 trimethyl hexoxy) diphenylamine p-n-octoxy phenyl-fl-naphthylamine pp'-di-n-decoxy diphenylamine 2,5 dimethoxy-4-n-octoxy diphenylamine m-n-hexadecoxy diphenylamine p-n-decoxy phenyl-B-naphthylamine.

When it is desired that the composition is a so-called Type II gas turbine lubricant, i.e. suitable for use at bulk oil temperatures of about 450 F., it is preferred that the ester is one of the so-called hindered esters which are derived from primary mono-, or poly-hydric (e.g. alcohols having from 2 to 10 or more OH groups),

alcohols in which there are no hydrogen atoms attached to the fl-carbon atoms. These alcohols thus contain one or more groups having the formula:

in which R and R are alkyl, hydroxyalkyl or etherified hydroxyalkyl radicals. These hindered esters have been found to exhibit exceptional thermal stability compared with the normal diester-type synthetic lubricants.

A particularly suitable class of hindered etsers are those derived from tri-methylolpropane, or pentaerythritol, substantially completely esterfied with one or more straight chain saturated monocarboxylic acids having from 4 to carbon atoms.

Examples of hindered esters which may be employed as the lubricating oil in compositions according to this invention are:

(A) Esters of 2,2-dialkyl substituted monohydric alcohols (2 mols) with dicarboxylic acids (1 mol).

(B) Esters of trimethylol ethane (1 mol) with monocarboxylic acid (3 mols).

(C) Esters of trimethylolpropane (1 mol) with monocarboxylic acids (3 mols).

(D) Esters of pentaerythritol (1 mol) with monocarboxylic acids (4 mols).

(E) Esters of dior tri-pentaerythritol (1 mol) with monocarboxylic acids (6 or 8 moles respectively).

(P) Complex esters prepared from neopentyl glycol (2 mols), dicarboxylic acids (1 mol) and monocarboxylic acids (2 mols).

(G) complex esters prepared from neopentyl glycol (1 mol), dicarboxylic acids (2 mols) and monohydric neo alcohols, e.g. 2,2,4 trimethyl pentanol (2 mols).

(H) COrnplex esters prepared from trimethylolethane or trimethylol propane (2 mols), monocarboxylic acids (4 mols) and dicarboxylic acids (1 mol).

(I) Complex esters prepared from pentaerythritol (2 mols), monocarboxylic acids (6 mols) and dicarboxylic acids (1 mol).

Examples of the dicarboxylic acids which may be used are adipic, azelaic, and sebacic acids and of the monocarboxylic acids butyric, valeric, caproic, caprylic, capric and pelargonic acids. The acids have to be chosen so that the resulting ester possesses the requisite physical properties, e.g. viscosity, pour point, and often mixtures of acids must be selected to provide a synthetic oil which will be suitable for the most exacting military specifications. If desired branched-chain mono carboxylic acids may be employed in the synthesis of the esters. Alternatively, blends of several different esters can be used.

Specific examples of hindered esters are:

Complex ester prepared from trimethylol propane (2 mols), caproic acid (4 mols) and sebacic acid (1" mol) Complex ester prepared from trimethylol propane mols), butyric acid (4 mols) and azelaic acid mol) Complex ester prepared from neopentyl glycol (1 mol),

6 sebacic acid (2 mols) and 2,2,4-trimethyl pentanol (2 mols) Many of the complex hindered esters prepared in this way are too viscous to be used as the sole lubricating oil in lubricants for aircraft gas turbine engines, but they may be employed in admixture with simple hindered esters, in an amount of, for example, from 1 to 70% by weight.

Alternatively blends of mixed esters may be prepared by esterifying a hindered alcohol with a mixture of acids in a wide range of proportions. Thus, for example, trimethylol propane (0.4 mol) was esterified with a mixture of caproic acid (0.5 mol) and capric acid (0.5 mol) until the reaction was complete. The product was further esterified with sebacic acid (0.1 mol) to yield a mixture of complex and simple esters. The product had a viscosity of 6.88 centistokes at 210 F. and a pour point of 60 F.

Certain esters derived from pentaerythritol are available commercially from the Hercules Powder Company under the registered trademarks Hercoflex and Hercolube. These esters are useful for blending in lubricating compositions for use at high temperatures.

Of the many types of hindered esters it is preferred to employ esters of trimethylol propane or pentaerythritol with straight chain monocarboxylic acids having from 4 to 10 carbon atoms.

One very suitable base fluid comprises a major proportion of a mixture of esters of trimethylol propane with straight chain monocarboxylic acids having from 4 to 9 carbon atoms together with a minor proportion, preferably from 530%, of a mixture of esters of dipentaerythritol with straight chain monocarboxylic acids having from 2-10 carbon atoms. Lubricants based on such blends have been found to be less prone to sludging than lubricants based wholly on trimethylol propane esters,

In those applications where the lubricating composition is to be employed at temperatures not exceeding about 350 F. maximum bulk oil temperature, the compositions according to the invention may be based upon a synthetic lubricating oil comprising one or more of the conventional-type diesters. Examples of these diesters which may be employed are:

Di-2-ethyl hexyl sebacate Di-3,5,5-tri methyl hexyl sebacate Di-iso octyl sebacate Di-Z-ethyl hexyl azelate Di-iso octyl azelate Di-iso octyl adipate Di-iso decyl adipate Di-iso tri decyl adipate These lubricating compositions which are employed at these temperatures are referred to as Type I compositions; they may contain from 1 to by weight of a substantially water-insoluble polyoxyalkylene glycol ether.

These polyoxyalkylene glycol ethers have the general formula RO(R O) R where R represents an alkyl group, R an alkylene radical, R is H or another alkyl group, and n is an integer. Preferably R represents a propylene radical or a mixture of propylene and ethylene radicals, suitable products being obtained by reacting propylene oxide or a mixture of propylene and ethylene oxides with an aliphatic monohydric alcohol or with a monoether of a glycol. The polyoxyalkylene chain may be composed, therefore, of alkylene radicals R of more than one kind. In the preferred ethers, where R is hydrogen, it will generally be necessary to have at least a proportion of propylene groups present in the polyoxyalkylene chain in order to obtain substantially water insoluble products.

Particularly preferred are the so-called LB series of synthetic lubricants sold under the registered trademark Ucon, these, it is understood, consisting of mixed polyoxypropylene glycol ethers containing one free hydroxyl group per molecule. For example, the two most viscous members of the LB series are especially suitable for use in selected compositions within the scope of this invention designed to comply with the British specification D. Eng. RD. 2487. Alternatively Ucon fluids of the socalled D series may be employed, e.g. Ucon DLB 20-E, these materials being diethers in which both R and R are alkyl groups. Similar materials to the Ucon D series are the Dow Ambiflo C series.

Compositions in accordance with the invention may include small amounts of benzotriazole and also small amounts of a dicarboxylic acid such as sebacic or azelaic acid.

If desired, minor amounts of, for example, up to 20% by weight on the weight of the composition of polyphenyl ethers may be employed; such compounds may be employed in compositions which are specifically designed as high temperature lubricants.

In certain instances, it may be desirable to have present in the composition one or more additives designed to increase the load-carrying capacity of the lubricant.

Compositions according to the invention may also contain copolymers which are well-known in the art as additives having sludge dispersant properties. Examples of such additives are copolymers of alkyl methacrylates, e.g. lauryl or higher methacrylates or mixtures of such methacrylates, with N-vinyl pyrrolidone and copolymers of long chain alkyl furnarates with vinyl acetate and N-vinyl pyrrolidone. These copolymers not only serve to disperse sludge and maintain the oil and the engine in a cleaner condition than would otherwise be obtained, but also in some cases appear to cooperate synergistically with the antioxidants giving overall better oxidation resistance. These copolymers may be used in the present invention in amounts of from about 0.2 to about 1.5% by weight on the weight of the composition.

A preferred composition in accordance with this inventi-on is a lubricating composition comprising an ester which has the formula:

$1120 CR CHsCHa-C-CHzO 0 OR" CHzOOCR' wherein R, R and R'" are the same or difierent straight or branched chain alkyl radicals having an average of from 6 to 9 carbon atoms, said ester having a viscosity at 210 F. from about 3.0 to about 5.0 es. and remaining free from crystallisation on storage at -40 F. for at least 72 hours, said ester having dissolved therein an N-alkoxymethyl or an N-cycloalkoxymethyl 3,7-dioctyl phenothiazine in an amount sufiicient to provide from 0.04 to 0.15 percent of sulphur together with from 1.5 to 2.5 percent of phenyl-a-naphthylamine.

When antioxidants are employed in accordance with the present invention in which, in the general formula, Ar and Ar are unsubstituted aromatic nuclei, a sludge dispersant copolymer is preferably also present. When, however, the preferred phenothiazine derivatives are employed, in which Ar and Ar are substituted by alkyl groups having a total of at least 8 carbon atoms, the use of sludge dispersant copolymers is rendered unnecessary. This is a considerable advantage since the copolymers are prone to both shear and thermal breakdown with a consequent reduction in viscosity of the lubricant.

Following is a description by way of example of compositions in accordance with the present invention.

EXAMPLE 1 Percent Ester A 95.4 Phenyl-a-naphthylamine 2.0 n-Hexoxymethyl phenothiazine 0.85 Acryloid HF 866 1.5 Benzotriazole 0.2 Sebacic acid 0.05

8 EXAMPLE 2 Percent Ester B 94.25 Phenyl-u-naphthylamine 1.5 p-n-Decoxydiphenylamine 1.0 N-n-decoxymethyl phenothiazine 1.0 Plexol 917 2.0 Benzotriazole 0.2 Sebacic acid 0.05

EXAMPLE 3 Percent Ester B 96.25 N-ethoxymethyl 3,7 dioctyl phenothiazine 1.5 Phenyl-a-naphthylamine 2.0 Benzotriazole 0.2 Sebacic acid' 0.05

EXAMPLE 4 Percent Mineral Oil A 62.0 Mineral Oil B 37.5 N-hexoxymethyl 3,7 dioctyl phenothiazine 0.5 EXAMPLE 5 Percent Mineral Oil A 60.0 Mineral Oil B 37.3 Butylene bis(2.4 di-t-butyl phenol) 0.5 N-methoxymethyl 3,7 dioctyl phenothiazine 0.2 Plexol 917 2.0

This composition Was of a type suitable for use as an ashless dispersant oil for piston-engined aircraft.

EXAMPLE 6 Percent Ucon LB 1145 98.69 N-cy-clohexoxymethyl 3,7 dioctyl phenothiazine 1.0 pp-Dioctyl diphenylamine 0.3 Benzotriazole 0.01

This composition was of a type suitable for use as a synthetic Worm gear lubricant conforming to S.A.E. (Society of Automotive Engineers) viscosity requirements. Ucon LB 1145 Was a polyoxypropylene glycol ether having a viscosity of about 38 cs. at 210 F.

EXAMPLE 7 Percent Di (2-ethylhexyl)sebacate 66.25 Ucon LB 1145 28.0 N-methoxymethyl 3,7 dioctyl phenothiazine 1.5 pp-Dioctyl diphenylamine 1.5 Aroclor 1254 2.4 CPS. concentrate 0.25 Benzotriazole 0.1

CPS. concentrate was a mineral oil solution containing approximately 20% of calcium petroleum sulphonate. Aroclor 1254 was a chlorinated diphenyl containing 54% chlorine.

This composition was of a type suitable for use as a Type I synthetic gas turbine lubricant for aircraft and had a viscosity of about 7.5 cs. at 210 F EXAMPLE 8 Percent Ester A 85.39 Ester C 10.0 Phenyl-a-naphthylamine 2.5 N-n-decoxymethyl 3,7 dioctyl phenothiazine 2.0 Benzotriazole 0.1 Sebacic acid 0.01

Ester C was a dipentaerythritol ester of mixed straight chain carboxylic acids having from 2 to 10 (average 6) carbon atoms.

This composition was of a type designed to meet the requirements of Pratt & Whitney Aircraft specification PWA 521-13 for a Type 11 gas turbine lubricant.

9' 1o EXAMPLE 9 were placed in a 2 litre round bottomedfiask and me- Percent chanically stirred for four hours at 9095 C. After Ester A 70.89 cooling, the reaction mixture was extracted with ben- Ester C 25.0 zene and the benzene was removed by distillation from Phenyl-a-naphthylamine 2.5 5 t a waterbath. The residue was taken up in boiling petro- N-methoxymethyl 3,7 dioctyl phenothiazine 1.5 leum ether (B.P. .40-60" C.) and filtered from a little Benzotriazole 0.1 unreacted phenothiazine. Evaporation of the petroleum Sebacic acid 0.01 ether left a liquid. residue that was purified by pouring to stirred methanol. The solid that separated was re- Thls composition is designed to comply with British Mmm o crystallised from petroleum ether (B.P. 40-60 lstry of Avlauon Specification D Eng RD 249 10 There were thus obtained 327 grams (52% yield) of EXAMPLE 10 a white crystalline solid melting at 80-825 C. which, ig z s on further recrystallisation, melted at 8282.5 C. gg gfi ygg gaggi g 5 tanoate 0 Preparation of N-n-decoxymethyl 3,7 dioctyl r n Methoxymethyl 3,7 dioctyl phenothiazine 0.75 phenothlazme 0 3,7 dioctyl phenothiazine (423 g. 1 mole) n-hexanol Thls composltlon had a viscosity of about 4 cs. at 210 F. and was a type designed to comply with US. military (221 g f Z 145 (a 80mm specification MIL-L-9236B which relates to relatively low form? 3 yde fi moe) and viscosity synthetic gas turbine lubricants designed to opermm dlhy rogen p Osphate d1 ydrate .Were ate at bulk oil temperatures of 0 R maximum heated under reflux for 1 hour. The reaction m1xture Examples 3 and inclusive, are typical of the pan was dissolved in petroleum ether and washed with water. ticularly preferred high temperature synthetic gas turdried Petrolwm l layer was evaPorated and the bine lubricants of the present invention. The thiazine resldue Pouredslowly Into Vlgorously Smred methaflol' derivatives herein disclosed may be prepared quite simply rfrhe Product l filtered, sucked dry and recrystanlsed b t' th' ha th ne al for ula mm lsopropan? y mac mg a lazme vmg e ge r In There was thus obtained 500 g. (85%) of white solid,

/H M.P. 9193 C. N Preparation of N-methoxyrnethyl 3,7 dioctyl phenothiazine 3,7 dioctyl phenothiazine (423 g., 1 mole), methanol (2. litres), 40% aqueous formalin (1 litre, 13 moles) and with the appropriate alcohol or phenol ROH and formsodium dihydrogen phosphate dihydrate (10 g.) were aldehyde under relatively mild conditions. A buifer such heated under reflux for 4 hours. The hot solution was as sodium dihydrogen phosphate dihydrate may be emfiltered and the methanol-insoluble solid so isolated ployed with advantage in some instances. The following (M.P. 150-160 C.) recrystallised from acetone. examples illustrate the preparation of typical thiazine de- 328 g. (70%) of solid, M.P. 173-174.5 C., was thus rivatives suitable for use as antioxidants in accordance isolated. with the present invention. Other thiazine derivatives in accordance with the pres- Preparation of N-n-hexoxymethyl phenothiazine lent mveimon i be prepared in a similar manner the preparative details and working up procedure differing Phenothlallne grams, 2 n-hexanol only slightly depending on the physical characteristics of g 4 40% aqueous formalin the product. Table I summarizes the properties and yields moles) and sodium dihydrogen phosphate (30 grams) ofanumber of the products so obtained.

TABLE I Thlaztnes of formula (EH10 R K fl R: s R, Ar=pheny1ene throughout. Nature of Analytical data Ref. Recrystallisation Yield M.P. 0.) Found (percent) Theoretical (percent) Code solvent (percent) Ar R1 R; R C H N S C H N S A21- H H 02H Ethanol 58 112-113 68.9 5.76 5.78 12.72 70.1 5.86 5.45 12.42

- 92 Liquid 4 53 11.20 4.91 11 23 52 80-82 5 4 53 9.91 4 71 10 24 61 8.68 24 10. 24 Acetone 6. 86 Iso-propanol 98 6. 65 57 6.28 76 5.96 92 5.39 76 4.54 80 4.54 53 5.65 62 5. 65 7-t-OBH17 B-t-CsHn i-CoHio B11 d0 7-t-C5H 7 3-t-C2H 1 i'CmHn 5 39 TABLE I-Continued Nature of Analytical date Recrystallisatlon Yield M.P. C.) Found (percent) Theoretical (percent) solvent (percent) R C H N S C H N S l-CraHar' 78 Liquid 1.97 2.21 CH: 91 112114.5 (Literature lVLP. 115 C.) CeHn 58 146-150 78. 8 9. (i8 2. 42 5. 88 79. 9. 98 2 (i2 5. 98 CoHs ca 142-14 2 56 6.50 6.04 CuHrCH: 76 104-108 81 2 9. 38 2 71 6.03 79.6 9.06 2.57 5 89 CrHsO C2114 75 45-50 6.29 2. 66 6.03 C a 75 ca 45 3.96 9.16 3.95 9.01 n-CioHn 88 Liquid 74. 1 9.41 3 49 7. 96 73.3 8.88 3.17 7. 25 E1 .Same as H -nn-C Hn 77 Liquid 3 14 7.63 3.00 6.85

A2. CioHnO *Further information as to the structure of the radical R is given in certain cases, as follows:

5 R=1, 3 dimethyl butyl. B7 R=oleyl, derived from commercial oleyl alcohol. B8 R =2-ethyl hexyl. B9 R=2,2,4 trimethyl pentyl. B10 R=3,5,5 trimethyl hexyl. I311 R=derived from mixed branched-chain primary decanols. B12 R=derived from mixed branched-chain primary tridecanols.

In order to demonstrate the suitability of the compounds of this invention and lubricating compositions containing them for use at high temperatures tests were carried out, the results of which are tabulated in Tables II to VII.

The test used to obtain the results recorded in Tables III to VII, inclusive was a modification of a test described by Baber, Cuellar and Lawler in a paper entitled Laboratory Tests for Evaluating Supersonic Transport Engine Lubricants and presented to the 1963 USAF Aerospace Fluids and Lubricants Conference at San Antonio, Tex. This was an extremely severe oxidation test in which air at the rate of approximately 196 litres/hour was blown through 350 mls. of the oil under test in a wide glass test tube, 64 mm. in diameter and fitted with a head containing a side arm, out of which volatile oxidation products distilled. In the modified test used in this work, the only catalyst was a steel specimen of 2 sq. in. total surface area.

TABLE II.-ROTARY BOMB OXIDATION TESTS AT 160 C. [All additives were dissolved in mineral oil A in 0.0025 molar In those cases where no recrystallisation solvent is listed, the substance crystallised directly from the methanol and was filtered ofi.

Compounds perfixed by B and C belonged to the class of novel compounds herein claimed, those prefixed by B being particularly preferred (D & E are novel also).

Other compounds which may be similarly prepared include methoxy methyl mono octyl 6,7 benzophenothiazine and methoxymethyl mono octyl 8, 9 benzophenothiazine.

does not mean, of course, that blends containing these lower proportions would not pass less severe tests.

TABLE III.-OXIDATION TESTS AT 450 Fl8 HOURS DURATION (AIR FLOW RATE 196 LITRES/HOUR) [Ester A was used throughout as base fluid] Phenyl-a- Viscosity in- Acidity in- Additive B5 naphthyl- Volatility crease (cs. crease (mg. (percent) amine loss (gm.) at 100 F.) KOH/gm.) (percent) (percent) None 2. 5 147 Very viscous 2. 5 None 127 Very viscous 2. 0 None 133 Solid 0.75 2. 5 86 74 3. 3 1.0 2. 5 63 47 2. 3 1. 5 2. 5 61 47 1. 9 2. 0 2. 5 62 54 2.0 2. 5 2. 5 66 60 1. 2 1. 0 2. 0 72 151 8. 6 1. 5 2.0 52 38 2. 1 2.0 2. 0 64 61 4. 8 2. 0 1. 5 99 694 12. 8 2.0 1. 0 116 4250 17. 4

Table IV demonstrates the effectiveness of a selection of the additives of the present invention when used in concentration] conjunction with phenyl-a-naphthylamine and shows that Additive Percent Induction Period equivalent proportions of the additives give similar re- (minutes) sults. It was noteworthy that the first four blends gave NM? 15 4 much drrtier tubes than the remarnder. Addmve o 7 15 TABLE IV.-OXIDATION 'rns'rs AT 450 F.18 hours duration A5 3 (AIR FLOW RATE 19s LITRES/HOUR) B2. 1.2 188 [Ester A was used throughout as base fluid and all blends contained B3 1. 27 131 2.5% phenyl-a-naphthylamlne] E1 1. 20 217 Viscosity increase Acidity increase Methylene bis 2,6-dl-t-buty1 Thiazine Percent (cs. at 100 F.) (mg. KOH/gm.)

phenol 1. 69 (percent) Table 11 above demonstrates the efiectiveness of the i i 0 82 42 1 5 additives of the present invention as antioxidants for 1 38 mineral oils. g? f;

These tests were carried out by the well known Rotary 37 Bomb (Wood River Bomb) oxidation test described in g Lubrication Engineering, January 1960, by G. H. von 1 45 Fuchs, in which 50 ml. of oil and 5 rrnl. of water were 57 1.86 52 2.9 sub ected to an atmosphere of oxygen at 85 lbs/sq. in 60 L90 42 L9 loading pressure in the presence of a catalyst consisting of g2 fig 5 metres of 14 S.W.G. copper wire. The bomb was ro- 1 63 tated in an oil bath at 160 C., the drop in pressure in 47 bolnb 'f recorded Contlnuously f f y- The All additives except B1 were present in sutficient amount to provide induction period was taken as that period of time over 65 about O the blendwhich a 25 lb./sq. in. pressure drop from the maximum pressure initially reached was recorded. Obviously the longer the induction period, the better the oxidation resistance of the oil under these test conditions.

, Table III demonstrates the effectiveness of a typical preferred additive of this invention when used in conjunction with phenyl-a-naphthylamine (PAN).

It will be seen here that the amount of PAN is critical, 1

good results being obtained with 2 or 2.5%, but progressively inferior results with lower proportions. This B1 was present in half this amount.

TABLE V.OXIDA'IION TESTS AT 450 F.-l8

DURATION (AIR FLOW RATE 196 LITRES/HO [Ester A was used throughout as base fluid and all blends contained HOURS UR) All amines were present in sufficient amount to provide about 0.128% N in the blend (due to the amine alone).

TABLE VI.OXIDATION TESTS AT 450 F18 HOURS DURA- TION (AIR FLOW RATE 196 LITRES/HOUR) Phenyl-A-naphthylamine (2.57) U Additive B5 (15%) in different hindered esters.

Viscosity increase Acidity increase Ester (cs. at 100 F.) (mg. KOH/gm.) (percent) 1. 85 63 0. 74 TMP tri-nheptanote. 15 1. 52 TMP tripelarg 56 9 Ester D 45 1.94 EsyteriJ E 32 1 26 77 ster B 3 1 5 a 5 Star 76 1.38 2472 Ester C TMP=tri-methylo1 pro one.

Ester D was a trimetiiylol propane ester of mixed straight chain carboxylic acids having predominantly from 7 to 10 carbon atoms.

Ester E was a trimethylol propane ester of mixed carboxylic acids having a viscosity of about'5.0 cs. at 210 F.

Ester F was a dipentaerythritol ester of mixed straight chain carboxylic acids, predominantly nbutyric, n-octanoic and n-decanoic acids.

fact, too dirty for viscosity to be determined, Whereas all the other blends gave viscosity increase of less than even though the test was conducted at 450 F. It should be noted that the two dispersant polymers employed were essentially similar chemically, Plexol 917 being in mineral oil, whereas Acryloid HP 866 was sup plied in di-Z-ethyl hexyl sebacate. It will be observed that very fair results were given by additive B5 without the use of a polymeric dispersant. At 425 F. results given by this additive are perfectly satisfactory in all respects.

We claim:

1. A lubricating composition consisting essentially of a major proportion of synthetic neutral organic carboxylic ester lubricating oil and a minor proportion of additives (a) and (b) as follows:

(a) N n decoxymethyl-3,7-dioctyl phenothiazine in such proportion to provide from 0.04 to 0.15% of sulphur by weight of the composition, and

(b) at least one secondary aromatic amine selected from the group consisting of phenyl-a-naphthyL amine, phenyl-B-naphthylamine, pp'-dioctyldiphenylamine, mixed heptyl dephenylarnines and compounds having the formula wherein Ar" is selected from the group consisting of a benzene nucleus and alkyl substituted derivatives thereof, Ar is a member selected from the group consisting of benzene and naphthalene nuclei and alkyl substituted derivatives thereof, R and R" are saturated alkyl radicals containing a total of from 8 to 20 carbon atoms, In is from 1 to 2 and n is from zero to 1, the proportions of the secondary aromatic amine being such as to provide from 0.1% to 0.2% of nitrogen by weight of the composition. 2. The composition of claim 1 wherein the additive (b) is phenyl-a-naphthylamine.

3. A composition as claimed in claim 1 wherein the lubricating oil is selected from the group consisting of TABLE V II.OXIDATION/CORROSI0N TESTS AT 450 F (48 HOURS) [All blends were based on ester A] Change in wt. of metal specimens Percent Acidity Thiazine Amines Dispersant Other (mg/sq. cm.) Vise. Increase (Percent) (Percent) (Percent) Additives Increase (mg. KOH/ (Percent) Ti Ag Cu Steel Mg A1 (cs. gm.)

100 F.) Phenothiazinc, 1.0 PAN, 1.0 Plexo1917, 2.0 Nil Nil -0 35 +0, 03 0 77 +0,04 1 7,2 Additive A2, 0.7. PAN, 0.5; Acryloid HF 866, Benzotriazole, 0.2; Nil +0.02 +0.03 +0.01 Nil Nil 16 5. 3

DODP, 1 0. 2.0. gtgacic acid, Additive A3, 0.8 PAN, 1.0. Acryloid HF 866, Benzotriazole, 0.2; Nil Nil +0.10 +0. 05 +0. 06 +0.03 21 9.8

1.5. Scbacic acid,

.05. Additive A4, 0.85 PAN, 1.0 Acryloid HF 806, Benzotriazole, 0.2; +0.01 Nil 0. 01 +0.03 +0.03 Nil 31.5 16.4

1.5. glelgacic acid,

.0 Additive B5, 2.0 PAN, 2.0 Be zot ia ole. 0.1; +0.04 +0.04 +0.01 +0.07 -0. +0.04 48 6.3

Szbjacic acid, 0. Additive B5, 2.0 PAN, 2.5 Be 0 1iaz01e,0-1; +0.20 +0.25 +0.40 +0.20 1.7 +0.50 44 5.9

Sebacic acid, 0.01.

1 Too dirty to determine.

PAN =Phenyl-a-naphthylamine.

D CDP =p-n-deooxy diphenylamine.

These oxidation/ corrosion tests were carried out in accordance with the procedure laid down in Pratt & Whitney Aircraft specification, PWA-521B, but at 450 F. instead of at 425 F. as required by that specification. In this test air is blown for 48 hours through 100 mls. of the oil contained in a wide glass test tube fitted with a reflux water condenser at a rate of 5 litres per hour in the presence of steel, silver, copper, aluminium, titanium and magnesium specimens suspended therein in the specified manner.

In the Pratt and Whitney specification, PWA-521B it is required that the specimens shall not change in weight by more than $0.30 mg./sq. cm. and that the viscosity at 100 F shall not increase by more than 50%.

It will be seen from the results in Table VII that the blend containing phenothiazine Was extremely dirty, in

esters derived from aliphatic primary monoand polyhydric alcohols having no hydrogen atoms attached to the carbon atom B to a hydroxyl radical and radicals and aliphatic monoand dicarboxylic acids, and mixtures of such esters.

4. A composition as claimed in claim 1 wherein the lubricating oil is selected from the group consisting of esters derived from trimethylol propane, pentaerythritol and dipentaerythritol substantially completely esterified with at least one saturated monocarboxylic acid having from 4 to 10 carbon atoms and mixtures of such esters, the ester and mixture of esters having a viscosity at 210 F. of from 3.0 to 6.5 centistokes.

5. A composition as claimed in claim 1 wherein the lubricating oil is selected from the group consisting of pentaerythritol tetravalerate, trimethylol propane tri-n- 15 heptanoate, trimethylol propane tripelargonate, trimethylol propane tricaprylate, pentaerythritol tetra-caproate, dipentaerythritol hexacaproate and mixtures thereof.

6. A composition as claimed in claim 1 wherein the lubricating oil consists essentially of at least one substantially neutral ester of a member selected from the group consisting of trimethylol propane, pentaerythritol and dipentaerythritol and monocarboxylic acids having from 4 to 10 carbon atoms.

7. A lubricating composition consisting essentially of a major proportion of an ester which has the formula:

wherein R, R" and R' are the same or difierent straight or branched chain alkyl radicals having an average of from 6 to 9 carbon atoms, said ester having a viscosity at 210 C. from about 3.0 to about 5.0 es. and remaining free from crystallisation on storage at 40 F. for at least 72 hours, said ester having dissolved therein N-ndecoxymethyl-3,7-dioctyl phenothiazine in an amount suflicient to provide from 0.04 to 0.15 percent of sulphur together with from 1.5 to 2.5 percent of phenyl-oi-naphthylamine.

8. A composition as claimed in claim 7 wherein a part of the ester is replaced by from to 30% by weight of an ester of dipentaerythritol and aliphatic carboxylic acids having from 2 to 10 carbon atoms.

9. A lubricating composition consisting essentially of a major portion of an ester which has the formula wherein R, R", R and R" are the same or different straight or branched chain alkyl radicals having an average of from 4 to 9 carbon atoms, said ester having a viscosity of from 4.0 to 6.5 centistokes at 210 F. and said ester having dissolved therein N-n-decoxymethyl 3,7 dioctyl phenothiazine in an amount sufiicient to provide from 0.04 to 0.15 percent of sulphur together with from 1.5 to 2.5 percent of phenyl-a-naphthylamine.

10. A lubricating composition as claimed in claim 1 wherein the lubricating oil is selected from the group consisting of esters having the formula:

COOR; (CH2):

OOORs wherein R and R are the same 'or difiereut and are branched-chain alkyl radicals having at least six carbon atoms, and x is from 4 to 8, and mixtures of such esters.

11. A lubricating composition as claimed in claim 10 wherein the ester and mixture of esters is selected from the group consisting of di(2-ethylhexyl) sebacate, di(2- ethylhexyl)azelate diisooctyl sebacate; 2-ethyl hexyl 3 :5 :5 trimethylhexyl sebacate, diisooctyl azelate, diiso octyl adipate, diisodecyl adipate and diisotridecyl adipate- 12. A lubricating composition which consists essentially of a mixture of from to 95 percent by weight of an ester of trirnethylol propane with straight chain carboxylic acids comprising from 70 to by weight of pelargonic acid; from 5 to 25% by weight of an ester of dipentaerythritol with mixed straight chain carboxylic acids having from 2 to 10 carbon atoms; from 2 to 3% by weight of phenyl-wnaphthylamine; from 1.5 to 2.5% by weight of N-n-decoxymethyl 3,7 dioctyl phenothiazine; from 0.05 to 0.15% by weight of benzotriazole and from 0.005 to .02% by weight of sebacic acid.

References Cited UNITED STATES PATENTS 2,930,758 3/1960 Tierney et a1. 252403 3,148,147 9/1964 Bell et al 252-475 3,218,256 11/1965 Edwards et al 25247.5 2,415,252 2/ 1947 Levi 260243 2,461,460 2/ 1949 Winnek et al 260243 2,526,118 10/ 1950 Charpentier 260243 2,836,564 5/1958 Roberts et a1. 252-475 2,897,152 7/1959 Elliott et al 25247.5 FOREIGN PATENTS 860,675 2/ 1961 Great Britain.

OTHER REFERENCES Murphy et al.: Mode of Action of Phenothiazine-type Antioxidants, Industrial and Engineering Chemistry, December 1950, pp. 24792489.

DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, L. G. XIARHOS, Assistant Examiners. 

1. A LUBRICATING COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF SYNTHETIC NEUTRAL ORGANIC CARBOXYLIC ESTER LUBRICATING OIL AND A MINOR PROPORTION OF ADDITIVES (A) AND (B) AS FOLLOWS: (A) N - N - DECOXYMETHYL-3,7-DIOCTYL PEHNOTHIAZINE IN SUCH PROPORTION TO PROVIDE FROM 0.04 TO 0.15% OF SULPHUR BY WEIGHT OF THE COMPOSITION, AND (B) AT LEAST ONE SECONDARY AROMATIC AMIANE SELECTED FROM THE GROUP CONSISTING OF PHENYL-A-NAPHTHYLAMINE, PHENYL-B-NAPHTHYLAMINE , PP''-DIOCTYULDIPHENYLAMINE, MIXED HEPTYL DEPHENYLAMINES AND COMPOUNDS HAVING THE FORMULA 